To enable increases in the recording density achieved by a magnetic head, the coercivity of the recording media must be increased to overcome the demagnetization field of the magnetic transition. However as the track width decreases, so does the head field. When a high-end hard disk drive (HDD) generates a high data transfer rate, in the order of 1 Gbit/s, or more, not only is greater head field strength required, but there also is a need for a faster flux rise time. In order to achieve a large enough overwrite value, even in such high frequency conditions, the write current is boosted, giving its waveform a large overshoot. This often brings about severe excess saturation of the head and, as a result, adjacent track erasures often occur.
FIG. 1 is a schematic illustration of a conventional planar write head while FIG. 2 shows a closeup of the vicinity of the pole tip region. The design implements a bottom pole 11 (P1), pedestal 12 (P1P) and small throat height region 13 (for flux concentration), which opposes plane top pole 14 (P2)across from write gap 15. These poles are made of soft magnetic materials such as Ni, Co, Fe or their composites. The coil layer is packed onto the P1, and the P2 pole is fabricated on a planar surface to allow good track width control for the P2 tip width definition. The write gap material is a non-magnetic conductor such Cu, Au, Al, Cr, Rh or their composite.
In a conventional planar write head, there are 3 kinds of flux leakage paths between the P1 and P2 pole at the air bearing surface (ABS), as shown is FIG. 3. Leakage path 31 is from P1 to P2, some of which contributes to writing on a magnetic medium. Leakage path 32 is flux flow from the P2 side to the P1 side wall. Leakage path 33 is flux from the P2 side wall to the PI P top boundary (P1 shoulder), because the P1 shoulder is coupled with the P2 side wall magnetically due to the structure. This flux path induces the concentration of the field just at the upper side of the P1 shoulder.
FIG. 4 shows cross track profiles 41-45 of the in-plane field at the upper side of the P1 shoulder for write currents (Iw) of 10, 20, 30, 40, and 60 mA, respectively. The x-axis cross track corresponds to the position illustrated in the lower portion of the figure. This Pl shoulder field has greater strength than the gap side field (from the P2 side to P1 side wall), and grows with a shallow peak around the P1 shoulder corner, from which the shoulder steps down gradually, as the write current increases. From this profile, the P1 shoulder field can become a possible source of erasures, not only at adjacent tracks but also at 2 or 3 tracks away.
The present invention discloses a way to remedy the undesirable problem of the P1 shoulder field in the high write current region.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,553,649, Santini shows recessing of the first pole. Cohen et al disclose etched regions around the first pole in U.S. Pat. No. 5,995,342 while Sasaki describes recessed regions around P1 in U.S. Pat. No. 6,317,289.